Expandable reamers are typically employed for enlarging subterranean boreholes. Conventionally, in drilling oil, gas, and geothermal wells, casing is installed and cemented to prevent the well bore walls from caving into the subterranean borehole while also providing requisite shoring for subsequent drilling operation to achieve greater depths. Casing is also conventionally installed to mutually isolate different formations, to prevent crossflow of formation fluids, and to enable control of formation fluids and pressure as the borehole is being drilled. To increase the depth of a previously drilled borehole, new and smaller diameter casing (such term including liner) is disposed within and extended below the previous casing. However, while adding additional casing allows a borehole to reach greater depths, the additional, smaller casing has the disadvantage of narrowing the borehole. Narrowing the borehole restricts the diameter of any subsequent sections of the well because the drill bit and any further casing must pass through the smaller casing. As reductions in the borehole diameter are undesirable because they limit the production flow rate of oil and gas through the borehole, it is often desirable to enlarge a subterranean borehole to provide a larger borehole diameter beyond previously installed casing to enable better production flow rates of hydrocarbons through the borehole.
A variety of approaches have been employed for enlarging a borehole diameter. One conventional approach used to enlarge a subterranean borehole includes using eccentric and bi-center bits. For example, an eccentric bit with a laterally extended or enlarged cutting portion is rotated about its axis to produce an enlarged borehole diameter. An example of an eccentric bit is disclosed in U.S. Pat. No. 4,635,738, assigned to the assignee of the present invention. A bi-center bit assembly employs two longitudinally superimposed bit sections with laterally offset axes, which when rotated produce an enlarged borehole diameter. An example of a bi-center bit is disclosed in U.S. Pat. No. 5,957,223, which is also assigned to the assignee of the present invention.
Another conventional approach used to enlarge a subterranean borehole includes employing an extended bottom-hole assembly with a pilot drill bit at the distal end thereof and a reamer assembly located at a proximal distance above. This arrangement permits the use of any conventional rotary drill bit type, be it a rock bit or a drag bit, as the pilot bit, and the associated extended nature of the assembly permit greater flexibility when passing through tight spots in the borehole, as well as the opportunity to effectively stabilize the pilot drill bit so that the pilot hole and the following reamer will traverse the path intended for the borehole. This aspect of an extended bottom-hole assembly (BHA) is particularly significant in directional drilling. The assignee of the present invention has, to this end, designed reaming structures as so-called “reamer wings,” which generally comprise a tubular body having a fishing neck with a threaded connection at the top thereof and a tong die surface at the bottom thereof, also with a threaded connection. U.S. Pat. Nos. 5,497,842 and 5,495,899, both assigned to the assignee of the present invention, disclose reaming structures including reamer wings. The upper midportion of the reamer wing tool includes one or more longitudinally extending blades projecting generally radially outwardly from the tubular body, the outer edges of the blades carrying PDC cutting elements.
As mentioned above, conventional expandable reamers may be used to enlarge a subterranean borehole and may include blades pivotably or hingedly affixed to a tubular body and actuated by way of a piston disposed therein as disclosed by U.S. Pat. No. 5,402,856 to Warren et al. In addition, U.S. Pat. No. 6,360,831 to Åkesson et al. discloses a conventional borehole opener comprising a body equipped with at least two hole-opening arms having cutting means that may be moved from a position of rest in the body to an active position by exposure to pressure of the drilling fluid flowing through the body. The blades in these reamers are initially retracted to permit the tool to be run through the borehole on a drill string and once the tool has passed beyond the end of the casing, the blades are extended so the well bore diameter may be increased below the casing.
The blades of these conventional expandable reamers utilize pressure from inside the tool to apply force radially outward against pistons which move the blades, carrying cutting elements, laterally outward. Still other conventional reamers utilize pressure from inside the tool to apply force axially against a piston which forces attached blades, carrying cutting elements, laterally outward. Still further, fluid-and pressure-operated expandable reamers are disclosed in U.S. patent application Ser. Nos. 11/875,241, 11/873,346, 11/949,259, and 11/949,627, each of which is assigned to the assignee of the present invention and the disclosure of each of which application is incorporated herein in its entirety by this reference, overcome some of the difficulties associated with conventional expandable reamers while providing for enhanced lateral movement of the blades.
Various approaches to drill and/or ream a larger diameter borehole below a smaller diameter borehole may include stabilizer blocks or pads used longitudinally above or below an expandable reamer to increase stability and reduce dysfunctional loads, i.e., lateral vibrational loading, thereupon while reaming. Use of stabilizers to improve the drilling performance of an expandable reamer is generally known to a person of ordinary skill in the art. In most instances, fixed stabilizer pads or blocks, being sized and configured for a corresponding hole diameter cut by a pilot bit or drill bit, are located in a drill string between the bit and the expandable reamer. It is recognized that an expandable reamer may be run through a borehole without a pilot bit or drill bit, particularly when reaming or expanding an existing borehole. The stabilizer pads or blocks help to control stability, particularly when conducting a so-called “down drill” operation, e.g., drilling in the down-hole direction. Also, as understood by a person of skill in the art, stability is further improved by providing a point of control above an expandable reamer to decrease the flexibility of the drill string about the expandable reamer. In this respect, an expandable reamer may include, when used in “down drill” operations, expandable stabilizer blocks or pads above the reamer. The expandable stabilizer blocks or pads are also known as expandable stabilizers, such as the movable bearing pad structure disclosed in U.S. patent application Ser. No. 11/875,241 referenced above, such apparatus being operated to an expanded state by the flow of fluid, such as drill mud, or pressure within the drill string. The expandable stabilizer blocks or pads may also be included in the drill string below the expandable reamer, either by replacing or augmenting the function of the fixed stabilizer pads or blocks. The expandable reaming blocks or pads, when placed above an expandable reamer, are conventionally sized and configured to extend to a diameter corresponding to the reamed borehole diameter.
The fixed and expandable stabilizer blocks or pads may be integral with a tool body of an expandable reamer or may be included with other down-hole tools serially connected above and/or below an expandable reamer, such as part of a drill bit or a stabilizer tool. The expandable reamers and the expandable stabilizers, operated by the flow of fluid or pressure within respective flow bores, overcome some of the limitations associated with bi-center and reamer wing assemblies in the sense that the pass-through diameter of such tools is nonadjustable and limited by the reaming diameter; and improves upon the tendency associated with conventional bi-center and eccentric bits to wobble and deviate from the path intended for the borehole. Moreover, the fluid-or pressure-operated expandable reamers and expandable stabilizers may overcome other limitations associated with conventional expandable reaming assemblies, such as being subject to damage when passing through a smaller diameter borehole or casing section, becoming prematurely actuated, and difficulties in removal through the casing after actuation.
Notwithstanding the various prior approaches to drill and/or ream a larger diameter borehole below a smaller diameter borehole, a need exists for improved apparatus, systems or methods for doing so. For instance, conventional systems for stabilizing while reaming a borehole (especially while back-reaming a drilled borehole) may encounter subterranean formation changes within the formation of the drilled borehole (i.e., a tight spot of swelled shale or filter cake in the formation, or other obstructions) making retraction of the stabilizer and reamer necessary while trimming or back-reaming, this being undesirable in that an under-gage borehole results. Thus, encountering changes in the previously reamed formation may necessitate deactivation (retraction) of an expandable reamer and stabilizer (particularly because the expandable reamer and stabilizer are activated, i.e., initially triggered, simultaneously by a single actuating device, i.e., a drop ball) in order to trip back up the borehole and then begin reaming again in the down-hole direction in order to trim the borehole to the proper diameter.
Accordingly, there is an ongoing desire to improve or extend performance of a stabilizer and reamer system having extensible blades and bearing pads for enlarging a subterranean borehole beneath a casing, including a method of use therefor. There is a further desire to provide a stabilizer and reamer system having extensible blades and bearing pads capable of independent, or consecutive, initial activation or triggering.